1. Field of the Invention
The present invention relates to antenna-matching devices, antenna devices and mobile communication terminals, and in particular relates to an antenna-matching device that is preferably used for an antenna of a mobile communication terminal such as a cellular phone, and also relates to an antenna device and a mobile communication terminal equipped with the antenna device.
2. Description of the Related Art
To date, in mobile communication terminals, a matching circuit has been used to perform impedance matching between an antenna and a power-feeding unit (including an RF circuit) that is connected to the antenna. As a matching circuit of this type, a technology is known in which elements that constitute a matching circuit are integrated into a multilayer substrate, as described in Japanese Unexamined Patent Application Publication No. 2004-336250. Moreover, a technique for forming a wide band antenna by coupling two radiating elements that make up a dipole antenna with each other through a coupling coil element is described in Japanese Unexamined Utility Model Registration Application Publication No. 62-24510.
If elements that constitute the matching circuit and the coupling coil element are mounted as separate components, the space that is used for mounting these components becomes large and it is difficult to use such a configuration in mobile communication terminals, for which size reduction is demanded. Furthermore, it is also necessary to match the impedances of these elements, which complicates the design of impedance characteristics.
On the other hand, an antenna including a base plate, a power feeding point and a monopole antenna radiating element, as illustrated in FIG. 15 of Japanese Unexamined Patent Application Publication No. 2007-282091, and an inverted-F antenna, as illustrated in FIG. 16 of Japanese Unexamined Patent Application Publication No. 2007-282091, are known examples of conventional antennas of a type that are to be built into terminal devices. However, these antennas have a narrow frequency band and it is difficult to use them in a wide frequency band.